JPH02776B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a substrate having an anti-reflection coating as defined below on at least one side and on which information bits can be written by means of a laser beam adjusted according to the information to be recorded. The present invention relates to an information recording element that has a laser beam and can be written and read using a laser beam. The anti-reflective coating has a reflective layer that reflects appropriate laser light, an absorbing layer that absorbs appropriate laser light, and a transparent layer interposed between the two layers that transmits appropriate laser light.

During recording, there is a difference between a value that is large enough to cause a physical change in the absorption layer of the information recording element and therefore does not satisfy the conditions for antireflection, and a value that is too low to produce this effect. Adjust the laser light to vary its intensity.

Information recording elements of the type mentioned above are described in West German Patent Application No. 2757737 (US Application No. 782032, 1977).
(March 28, 2016; Dutch Patent Application No. 7713230)
has been disclosed.

Conventional information storage elements are assembled from a substrate (for example made of glass) which is provided with a reflective layer (for example made of aluminum). A transparent layer of silicon dioxide is provided on the reflective layer and an absorbing layer is provided on top of this. This absorbing layer can be made of dye or metal. In the case of a dye, the optical density of the dye changes locally during the writing of information. On the other hand, if the absorption layer is made of metal, cavities are burned into it. The reflective layer, the transparent layer and the absorbing layer together form an anti-reflective coating, and these three layers match each other in material thickness and properties to satisfy the anti-reflective requirements. Laser light is not reflected during recording. Almost all the energy of the laser light is absorbed by the absorption layer of the anti-reflection coating.

An object of the present invention is to further improve conventional information recording elements. The recording element of the invention ensures that the energy applied during writing of information is not only absorbed as completely as possible in the absorption layer of the anti-reflection coating, but also as much as possible in the areas where it is necessary to cause physical or chemical changes in the absorption layer. Because steps have been taken to ensure concentration, the sensitivity is higher than the conventional elements described above. This means that information can be written to the information recording element using laser light of lower intensity (or faster speed if the same intensity is used).

The invention is based on the recognition of the fact that some portion of the energy applied when writing information with laser light is emitted through the transparent layer by thermal conduction. This emitted portion of energy does little to cause physical or chemical changes in the absorbing layer. If the transparent layer is made of a material that conducts heat over a smaller area, a larger portion of the total irradiation energy of the laser light is utilized to cause the desired physical change. Compared to the description in German Patent Application No. 2812868, it does not seem necessary to take measures for rapid heat release in the transparent layer in order to prevent the transparent layer and the reflective layer from being damaged.

Furthermore, the present invention relates to an information recording element as described in the preface, in which the transparent layer is formed at room temperature.
It is characterized by containing an organic compound that has a thermal conductivity of 0.7 W/mK or less and transmits appropriate laser light.

Generally, organic compounds have a thermal conductivity that is one-tenth or less of that of silicon dioxide, which has been used so far. Suitable organic compounds include PVC, polyester,
Polymeric compounds such as polyethers and polyolefins. Especially useful are photocurable lacquers, such as acrylate-based solventless lacquers. Dutch Patent Application No. 7611395 (PHN8576) by the same applicant as an example of a photocurable lacquer
There is a description in . Organic compounds can be deposited by spinning, sputtering, CVD (chemical vapor deposition), and the like. Most polymers are deposited by spinning. Alternatively, organic dyes that transmit the applied laser light can be successfully used as organic compounds. Usually organic dyes can be deposited by vapor deposition. When using diode laser light (800-870 mm), satisfactory results are obtained using vapor-deposited phthalcyanine ( _C32H18N8 ) or cetocyanine as _a transparent _interlayer .

The information recording element is read by reflected light. During readout, reflection of the incident laser light occurs because the antireflection conditions are not satisfactory in areas where physical or chemical changes have occurred in the absorbing layer. This reflected laser light can be detected. Prior to the present invention, the absorbing layer was placed as far away from the substrate as possible. That is, a reflective layer of antireflection coating was provided in contact with the substrate. However, a particularly suitable example of an information recording element is obtained if the absorbing layer of the antireflection coating is provided as close to the substrate as possible.
In this case, the information recording element is reflected through the substrate.
It is necessary to read it. Next, of course, the substrate must be transparent to the laser light used. The fact that this example - also when the absorbing layer is made of metal - gives satisfactory results is surprising. If holes are created mechanically in the absorption layer, it is expected that metal removal will be difficult because the absorption layer is enclosed between the substrate and the transmission layer. However, in practice no significant difficulties are encountered. This example has the advantage that external damage to the information recording element is outside the focal length of the object that focuses the laser light onto the absorption layer. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a reference example information recording element in which information is already stored. S indicates a substrate. Anti-reflection coating includes reflective layer R and transparent layer T.
and an absorbent layer A. 1 indicates a physical change, that is, a hole, which is provided in the absorption layer. Again for completeness, the properties of transparency, reflection and absorption are matched to the wavelength of the laser light used. It is possible to use materials that do not have or have only a few of the above-mentioned properties when irradiated with different wavelengths.
The substrate S can be manufactured from various materials, such as glass, synthetic resin materials, etc. Although the substrate can be transparent, this is not mandatory in the example shown in FIG.

A reflective layer R is provided on a substrate S. R can be composed of metals such as aluminum and silver. These metals can be easily deposited onto a substrate by vapor deposition. Alternatively, a self-reflecting substrate S can be used, and the reflective layer R can be made coincident with the substrate S. Alternatively, a multilayer or single layer dielectric reflector can be used for layer R.

Next, a transparent layer T is provided on the layer R. Layer T is made of organic material. Suitable organic materials include polymeric substances,
For example, polyvinyl chloride, polyester of ethylene glycol and terephthalic acid (Mylar), polytetrafluoroethylene (Teflon), poly-p-
There are xylene (parylene), cellulose, and others.
Many polymeric substances require deposition on layer R in solution form followed by evaporation of the solvent. The method of depositing this layer is often cumbersome. Spinning lacquer that can be easily hardened,
After being applied by dipping or similar methods, it is cured to a solid polymer by UV irradiation. On the substrate, Teflon can be deposited by sputtering and parylene can be deposited by thermal dissociation of the dimer and condensation and polymerization of the generated radicals. Alternatively, the organic material can be a dye that transmits the laser light used. The use of organic dyes is advantageous since they can mostly be applied by simple vapor deposition methods. Even if the dye decomposes during vapor deposition, organic deposits suitable for the present invention can be obtained. This can be applied in particular by vapor deposition of Sudan black. Suitable dyes include, for example, setocyanine, sudan black and especially phthalcyanine.

Absorbent layer A is applied on top of layer T. Layer A can consist of a thin metal layer, such as a pismuth-titanium or rhodium layer. What is actually appropriate
A thin layer of Cd or Zn, for example a 5 nm thick Zn layer. The metals Zn and Cd have low melting points and are corrosion resistant at room temperature, but additionally dye layers such as vanadyl phthalcyanine layers can be used.

Layers R, T and A must be interrelated to satisfy anti-reflection requirements. That is,
When laser light enters the absorption layer A from the direction indicated by the arrow in FIG. 1, part of the light is reflected, part is absorbed, and the other part is transmitted. The transmitted part is reflected by the reflective layer R, then part is absorbed by the layer A, and part passes through the layer A and is emitted to the outside. If the last part - the part emitted to the outside - and the part that enters and is reflected by layer A are in opposite phase, the part emitted to the outside partially annihilates the part reflected by layer A. . This partial annihilation occurs if the thickness of the transparent layer T is chosen depending on the reflectivity of the materials used for the layers R, T and A, with the beam incident at A and reflected at R and the outside The phase difference between the beam and the beam emitted at is equal to an odd multiple of π. If we ignore the correction for the phase change upon reflection at A and R and ignore the constant thickness of A, the thickness of the intermediate layer is 1/4λ(2n+
1), λ is equal to the wavelength of the laser light in the medium, and n is an integer greater than or equal to zero. Taking into account the predominance of heat loss through the reflective layer, the layer thickness is preferably chosen to be sufficiently thick (through the choice of n) that no heat is diffused from the absorbing layer to the reflective layer during the irradiation phase. . The conditions for antireflection are known per se. Reference books on information recording devices include ``Antireflection Structures for Optical Recording'' by A. E. Bell and F. D'Avrill Spong (A.
E・Bell and FWSpong, Anti reflection
Structures for Optical Recording, IEEE
Journal of Quantum Electronics, Volume QE14, No. 7, July 1978, pp. 487-495).

FIG. 2 is a diagram showing an embodiment of the information recording element of the present invention. The letters and numbers in FIG. 2 have the same meanings as in FIG. In this embodiment, the substrate must be transparent so that it can be written to and read from by laser light incident from the direction indicated by the arrow. When writing and reading information, the laser beam is focused on the absorption layer A, which in this embodiment is sealed inside the information recording element and protected from damage. If the free surface area of the substrate is damaged, there is no harm since this free surface area is outside the depth of the focal range of the target on which the laser light is focused. In the example shown in FIG. 1, layer A is susceptible to damage and damage.

The use of the information recording element of the present invention will be further explained with reference to FIG.

The laser beam indicated by the arrow is directed toward the information recording element. The intensity of the beam is adjusted between a value large enough to burn out hole 1 in layer A and a value not large enough to burn it out, depending on the information to be recorded. moving the laser beam relative to and/or against the information recording element; In this way, a pattern of holes 1 or physical or chemical changes is obtained in layer A, but one of these changes
Only the species are shown in the figure. During reading, a lower intensity laser beam is used, so no more holes are created in layer A. When the laser beam is incident on the hole 1, it is reflected, but when the laser beam reaches the vicinity of the hole, it is not reflected at all or is reflected slightly. The reflected light is detected and further processed. , In addition to the layers mentioned above, the recording element of the invention may further include other layers such as a protective layer.

Experimental Example 1 An aluminum reflective layer was deposited on a 1 mm thick glass substrate (50 nm thick). 140nm thick poly-p
-Polymer layer of xylene (thermal conductivity at room temperature
0.2 W/mK) was applied onto aluminum by thermal dissociation.

An absorbing layer of Bi with a thickness of 8 nm was deposited on the polymer layer. In the device thus obtained, holes were burnt out in the absorption layer by a diode laser (wavelength 820 nm) using an energy of 60 mW for 50 ns. When using a layer of SiO ₂ with a thickness of 140 nm (instead of a polymer layer), an energy of 20 mW was required.

Experimental Example 2 A layer of vanadyl phthalcyanine (20 nm thick) was vacuum deposited on a substrate as an absorbing layer. After that, a cellulose layer (300nm) (conductivity 0.25W/at room temperature)
mK or less) was deposited by spinning. Finally, an aluminum reflective layer was vacuum deposited onto the cellulose. 20mW in 100ns through the substrate to the absorption layer
Krypton laser (λ=672n
Due to the physical/chemical changes caused by m), the irradiated area did not quickly satisfy the anti-reflection condition.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of an information recording element as a reference example;
The figure is a sectional view of an embodiment of the information recording element of the present invention. S...substrate, R...reflective layer, T...transparent layer, A
...Absorption layer, 1 ... hole.

Claims (1)

[Claims] 1 a substrate with an anti-reflection coating on at least one side, on which information bits can be written by a laser beam adjusted according to the information to be recorded, the coating reflecting the appropriate laser beam; reflective layer, absorption layer that absorbs appropriate laser light,
In the information recording element, which has a transparent layer provided between these two layers and allows appropriate laser light to pass therethrough, and can write and read information using the laser light, an absorption layer is provided on the substrate, and the absorption layer is provided on the substrate. a transparent layer is provided on the layer, a reflective layer is provided on the transparent layer, the substrate is transparent, and the transparent layer has a thermal conductivity of 0.7 W/mK or less at room temperature and is suitable for laser radiation. An information recording element characterized by being made of an organic compound that transmits light.